Why does it flip me around and around (First Person)

I had this working a few weeks ago and I have and used the same code in another project and it flips me around and around. The 'Player' is a empty game object and has a capsule collider, rigid body attached to it and the character controller attached to it plus this code. (the 'player' also within its folder thingy/under the 'player' is the camera and 3d object capsule connected to it) Any help would be most appreciated! Code:

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class PlayerController : MonoBehaviour {

 [SerializeField] Transform playerCamera = null;
 [SerializeField] private float mouseSensitivity = 3.5f;

 [SerializeField] private float movementSpeed;

 [SerializeField] private float walkSpeed;
 [SerializeField] private float runSpeed;
 [SerializeField] private float runBuildUpSpeed;
 [SerializeField] KeyCode runKey;

 [SerializeField] float gravity = -25.0f;

 [SerializeField] [Range(0.0f, 0.5f)] float moveSmoothTime = 0.3f;
 [SerializeField] [Range(0.0f, 0.5f)] float mouseSmoothTime = 0.03f;

 [SerializeField] bool lockCursor = true;

 private float cameraPitch = 0.0f;
 private float velocityY = 0.0f;
 CharacterController controller = null;

 Vector2 currentDir = Vector2.zero;
 Vector2 currentDirVelocity = Vector2.zero;

 Vector2 currentMouseDelta = Vector2.zero;
 Vector2 currentDeltaVelocity = Vector2.zero;

 private void Start()
 {
     controller = GetComponent<CharacterController>();
     if (lockCursor)
     {
         Cursor.lockState = CursorLockMode.Locked;
         Cursor.visible = false;
     }
 }


 private void Update()
 {
     UpdateMouseLook();
     UpdateMovement();
 }

 private void UpdateMouseLook()
 {
     Vector2 targetMouseDelta = new Vector2(Input.GetAxis("Mouse X"), Input.GetAxis("Mouse Y"));

     currentMouseDelta = Vector2.SmoothDamp(currentMouseDelta, targetMouseDelta, ref currentDeltaVelocity, mouseSmoothTime);

     cameraPitch -= currentMouseDelta.y * mouseSensitivity;
     cameraPitch = Mathf.Clamp(cameraPitch, -90.0f, 90.0f);

     playerCamera.localEulerAngles = Vector3.right * cameraPitch;
     transform.Rotate(Vector3.up * currentMouseDelta.x * mouseSensitivity);
 }

 private void UpdateMovement()
 {
     Vector2 targetDir = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
     targetDir.Normalize();

     currentDir = Vector2.SmoothDamp(currentDir, targetDir, ref currentDirVelocity, moveSmoothTime);

     if (controller.isGrounded)
         velocityY = 0.0f;

     velocityY += gravity * Time.deltaTime;

     Vector3 velocity = (transform.forward * currentDir.y + transform.right * currentDir.x) * movementSpeed + Vector3.up * velocityY;

     controller.Move(velocity * Time.deltaTime);

     SetMovementSpeed();
 }

 private void SetMovementSpeed()
 {
     if (Input.GetKey(runKey))
         movementSpeed = Mathf.Lerp(movementSpeed, runSpeed, Time.deltaTime * runBuildUpSpeed);
     else
         movementSpeed = Mathf.Lerp(movementSpeed, walkSpeed, Time.deltaTime * runBuildUpSpeed);
 }

}